Electric lamp



J. DANA 2,317,035

ELECTRIC LAMP l April 2o, 1943.

Filed March 28, 1941' 93A IIIIIIIIA'IA'IIIIIII lrwentora:

Jurwius Drwa,

Their Attorneg.

Patented Apr. 20, 1943 ELECTRIC LAIYII.

Junius Dana, University Heights, Ohio, assigner to General ElectricCompany, acorporation o! l New York Application March 28, 19441, SerialNo. 385,672

'1 Claims.

My invention relates in general to electric light projection devices ofthe type in which a small electric lamp, such as an incandescent lamp,is mounted within a sealedpenclosure comprising a reflector member and acover glass or lens united thereto in an airtight manner. Morespecifically, my invention relates to electric Aincandescent lamps forsuch light projection devices, and particularly to the base constructionof such lamps.

Automobile headlamps of the so-called Sealed Beam type have recentlycome into Widespread commercial use. In one form of such type headlamps,hereinafter referred to as metal reflector lamps, a small electricincandescent lamp is mounted within an enclosure formed of a metalreflector section of parabolic or other suitable shape and a glass coveror lens section clamped or otherwise secured at its periphery to themetal reflector section in an airtight manner. The base of the electricincandescent lamp extends through an opening in the metal reflector, andthe annular space between the lamp base and the reflector opening isfilled with solder or other suitable material so as to secure the lampin place within the enclosure and at the same time form a hermetic sealbetween the lamp base and the metal reflector.

whereby ingress of foreign matter thereinto is eliminated. However, inpractice, it has been found that such is not .the case. Thus, it hasbeen found that the basing cement which is usually employed forattaching the base of the incandescent lamp to the glass bulb thereof ismore or less porous in nature, with the result that foreign matter iseventually drawn into the headlight enclosure, durlng the use of theheadlamp, under the influence of the alternate heating and cooling ofthe atmosphere Within the headlamp. Y

When the atmosphere within the enclosure of such metal headlamps becomesheated, such as is occasioned by the heat radiated by the incandescentlamp during operation of the same, or by the exposure of the headlamp tothe sun on hot days, the pressure of the atmosphere within the headlampenclosure increases to a point above that of the external atmospherewith the result that a portion of the internal atmosphere is driven outthrough the porous basing cement.

Then, when the headlamp cools down upon discontinuance o! lamp operationor discontinuance of the heating action of the sun, the pressure of theatmosphere within the headlamp enclosure decreases to a point below thator the external In this manner the headlamp enclosure is presumablyrendered airtight atmosphere so that the resulting partial vacuum withinthe headlamp enclosure draws a quantity of the outside atmosphere intothe enclosure, the foreign matter entrained or otherwise present in suchatmosphere being drawn along therewith into the enclosure. Due to therepeated occurrence of such action during usage of the device,additional foreign material is drawn into the headlamp enclosure fromtime to time, with the result that the reflecting surface of theheadlamp gradually becomes tarnished so as to decrease the efliciency ofthe device. The tarnishing action is particularly noticeable in smokyregions where a relatively high percentage of sulphur vapor is presentin the atmosphere, such vapors being particularly detrimental to thereilecting surface. In addition, the water vapor which is present in theoutside atmosphere, is drawn into the headlamp enclosure and condenses,from time to time, on the inner surface of the headlamp lens where itmaterially impairs the distribution of the light rays from the headlamp.

According to the invention, the above-mentioned disadvantages have beenovercome by providing a hermetic seal between the base and the bulb ofthe incandescent lamp employed in such light projecting devices wherebythere is no path for passage of the atmosphere into and out of theheadlamp venclosure through the end of the lamp base and the annularspace between the sleeve of the lamp base and the neck of the lamp bulb.

One object of my invention is to provide an electric light projectiondevice of the above mentioned type having a hermetically Asealedenclosure whereby ingress of foreign material thereinto is eliminated.

Another object of my invention is to provide an electric lightprojection device of the above mentioned type in which a hermetic sealis provided between the glass bulb and the outwardly extendingbase ofthe electric lamp mounted in such device.

Still another object of my invention is to provide an electric lamphaving a hermetic seal between the base and bulb thereof so as toprevent the passage of a gaseousmedium through the end of the base andthrough the annular space between the base shell and lamp bulb.

A feature of the invention is the provision of a compound basing ,cementfor an electric lamp composed of two separate and distinct compositions,one of which functions to provide a bond of suiiicient strength betweenthe base and lamp bulb to withstand normal handling stresses, and theother of .which functions to provide an airtight seal between the baseshell and the bulb neck.

Further objects and advantages of my invention will appear from thefollowing description of species thereof and from the accompanyingdrawing in which:

Fig. 1 is a vertical section of an electric light projection deviceaccording to my invention; Fig. 2 is a fragmentary sectional view, on anenlarged scale, of the base construction of an electric incandescentlamp comprising my invention for use in the light projection deviceshown in Fig. 1; and Figs. 3 and 4 are views similar to Fig. 2 ofmodified forms of electric incandescent lamps according to my inventionfor use in the light projection device shown in Fig. 1.

Referring to Fig. 1. the light projection device there shown comprisesan enclosure I formed of a metal reflector member II and alight-transmitting cover member or lens I2 of suitable material, such asglass, secured together at their peripheries or rim portions I3 and I4,respectively.'

by suitable means forming an airtight joint, a rubber gasket I5 beinginserted between the opposing i'fm portions I3. I4 and compressedtherebetween so as to form an airtight seal between the parts. As shownin the drawing, the reflector Il and lens I2 are preferably securedtogether by means of a flange I6 extending forwardly from the outer edgeof the rim I3 on the metal reflector and rolled over onto the topsurface of the rim I4 of the lens I2 while the parts are in assembledrelation with the rubber gasket I5 under compression. The reflector IIis preferably formed as a paraboloid having a focal length ofapproximately 11/8 inches, but obviously it may be formed of any othersuitable reflecfor shape. The inner surface of the reflector II isprovided with a coating I1 of aluminum, silver, or any other suitablereflecting material. The cover member I2 is preferably formed as a lenshaving suitable light-directing iiutes and prisms I8 on its innersurface to provide the desired distribution of light from the device. Atlts apex, the metal reflector II is provided with an opening I9 whichmay be bordered by a rearwardly extending, outwardly flaring ange 20.Instead of extending rearwardly, the flange 20 may be turned inwardly(i, e.. forwardly). It will be understood, however. that the use of suchaflange at all is entirely optional. The base 2I of a small electricincandescent lamp 22 extends out through the opening I9 and is securedto the reflector I I by a ring 23 of solder which completely fills theannular space between the shell 24 of the lamp base 2I and the reflectorflange 20. The ring of solder 23 maintains the lamp in place within theenclosure and provides a hermetic seal between the lamp base 2I `and thereflector II.

The incandescent lamp 22 is of a type similar to that described andclaimed in U. S. Patent 2,227,324, Severin, issued December 31, 1940,and comprises, in addition to the base 2|, a glass bulb 25 having a neckportion 26 secured to the base 2I by a ring of basing cement 21 andprovided with a reentrant stem 28. Mounted within the bulb 25 are a pairof concentrated ,filaments 219, 30 each consisting of a linear coil oftungsten or other suitable refractory metal. The filaments 29, 30 extendtransversely of the axis of the bulbl 25 and parallel to one another,and are spaced apart vertically a distance of approximately 0.100

inch and, in addition, are offset laterally a dlstance of 'approximately0.105 inch with respect to one another. The lamp 22 is mounted in theparabolic reflector II with the filaments 29, 33 disposed horizontally,with the lower filament 29 arranged symmetrically about the focus of thereector II. The filaments 29, 30 are supported by, and are electricallyconnected to, three leading-in wires 3I (one common to both filaments)which are sealed into the press portion 32 of the stem 28 and extendtherethrough to the terminals 33 4of the lamp base 2|. The saidterminals are suitably fastened to a disc of insulating material 34mechanically secured to and closing the outer end of the lamp base shell24.

In accordance with the invention, the passage of a gaseous medium, suchas the atmosphere. through the lamp base 2| and into the headlampenclosure I 0 is effectively prevented by the prosuch a gaseous mediumthrough the lamp base.

In this manner, the ingress of foreign material into the headlampenclosure is prevented so that tarnishing of the reecting surface I1,and condensation of water vapor within the enclosure on the opticalsurfaces of the headlamp. are eliminated.

The hermetic sealing of the lamp base is preferably effected by means ofa suitable sealing medium or compound disposed within 0r across theannular space between the shell 24 of the lamp base and the neck 26 ofthe lamp bulb, as shown particularly in Figs. 2 to 4. In sealing thelamp base by this method, a composite basing cement is preferablyemployed for attaching the lamp base 2| to the bulb 25, the cement beingcomposed of two separate and distinct portions of different compositionseach of which performs a separate and distinct function. Thus, as shownin Figs. 2 to 4, the lower portion 35 of the ring of basing cement 21(i. e., that portion closest t0 the termi.l

nal end of the base) is formed of a composition which provides a bond ofthe necessary mechanical strength to withstand the stresses to which itmay be subjected during the normal handling and usage of the lamp, whilethe upper portion 36 of the basing cement 21 (i. e., that portionadjacent the rim or edge of the base shell 24) is formed of acomposition which will effectively seal the annular space between thebase shell 24 and the bulb neck 26 against the passage therethrough ofany and all gaseous mediums.

The lower bonding cement portion 35, which serves as the means forfastening the base to the bulb, fills the greater portion of the annularspace between the base shell 24 and the bulb neck 26 so as to provide abond of maximum strength therebetween, while the sealing portion 36 needonly consist of a relatively small ring of material of sufilicientsection to insure an effective hermetic sea The bonding cement 35 usedto secure the lamp base 2l to the bulb 25 is of the type commonlyemployed for such purposes comprising an inorganic filler, such aspowder of marble, alumina. or magnesia, mixed with a suitable bindingagent or agents, such as shellac, rosin, and suitable synthetic resins,for example, "Bakelite or Durite." Such type basing cements are more orless porous in nature, so that in the absence of a hermetic seal in thelamp base, the outside atmosphere slowly penetrates through the basingcement and enters the headlamp enclosure I0.

'I'he sealing material 36 may consist of any vcially known as appliedequally vide a hermetic seal, and whichpossesses the necessaryresistance toflow at the operating temperature of the lamp. Thus, I havefound that a synthetic resin, such as 'that commercially known as AYABor AYAT vinylite (made by the Union Carbide and Carbon Corporation) withor without a suitable iiller such as that commer- Asbestine, willprovide a satisfactory seal if used in sections of suflicient thickness.The material preferably employed for the 'sealing cement, however, isone which is thermosetting in character, i. e., one which doesnotresoften under heat once it has been cured. As an example of such amaterial, I have found a solution of urea formaldehyde, modified with anondrying alkyd to prevent brittleness, to be particularly advantageous.The urea formaldehyde solution is applied to the junction of the baseand bulb of a finished lamp, after which lthe material is dried at roomtemperatures or above until the solvent is removed, and then cured for alength of time depending on the temperature used. Since this materialdoes not resoften at the operating temperature of the lamp, a relativelythin section may be used to provide a seal against pressure.

Obviously, instead of the urea formaldehyde gum referred to above, othersuitable thermosetting gums may be used, such as the phenol formaldehydeand phenol uriurol class of gums, or the gum commercially known asMelamine, manufactured by The American Cyanamid Company; or variousmixtures oi such gums, Athe urea formaldehyde class included, may beused, an alkyd-resin or other suitable non-drying material beingpreferably added in each case to prevent b-rittleness of the iinalproduct.

As shown in Fig. 2, the sealing material 36 may be applied to thejunction between the edge of the base shell 24 and the bulb 25, thematerial preferably extending a short distance down onto the outersurface of the base shell adjacent the edge v thereof. Alternatively,the sealing material 36 may be disposed entirely within the base shellin the form oi a ring of the material located immediately adjacent theedge of the base shell, as shown in Fig. 3; or a small portion of thebase shell 24 at the outer edge thereof, may be flared outwardly, asindicated at 38 in Fig. 4, to conform more or less to the curvature ofthe bulb wall, and the sealing material 36 disposed within the annularspace between the said flaring edge portion 3B and the wall of the bulb25.

It will be obvious that .the invention may be as well to an electriclamp wherein the base is attached to the bulb by mechanical meansinstead of by the conventional basing cement as described hereinabove.

What I claim as new and desire to secure by. Letters Patent of theUnited States is:

1. A light projecting device comprising an airtight enclosure, anelectric lamp sealed within said enclosure comprising a bulb having aneck portion and a base having a shell portion enclosing saidneck-portion and secured thereto, said base extending out vthrough thewall of said enclosure and hermetically sealed thereto, and a sealingcompound disposed adjacent the junction between said base shell and bulbfor hermetically sealing the space therebetween to prevent leakage ofair into said enclosure through the interior of said lamp base.

2. An electric lamp comprising a bulb having a neck portion and a baseenclosing said neck portion and secured thereto by a composite basingcement having portions of diierent compositions, one of said portionsbeing of a composition providing a bond of the required mechanicalstrength between said base and bulb to hold said parts together and theother of said portions being of a composition providing a hermetic sealbetween said base and bulb. x

3. An electric lamp comprising a bulb having a circular neck portion, acylindrical base enclosing said neck portion and secured thereto by aring of basing cement disposed within the annular space between saidbase and neck portion, and a sealing compound disposed adjacent thejunction between said base and bulb and covering the exposed surface ofsaid ring of basing cement for hermetically sealing the said annularspace between said base and bulb neck.

4. A light .projecting device comprising an airtight enclosure, anelectric lamp sealed within said enclosure comprising a bulb having aneck portion and a base having a shell portion enclosing said neckportion and secured thereto, said base extending out through the wall ofsaid enclosure and hermetically sealed thereto, and a. thermo-settingsealing compound disposed adjacent the junction between said base shelland bulb for hermetically sealing the space therebetween to preventleakage of air into said enclosure through the interior of said lampbase.

5. A light projecting device comprising an airtight enclosure, anelectric lamp sealed within said enclosure comprising a bulb. having aneck portion and a base having ashell portion enclosing said neckportion and secured thereto, said base extending out through the wall ofsaid enclosure and hermetically sealed thereto, and a sealing compoundcomposed of 'a thermo-setting gum modified with a nondrying alkyddisposed adjacent the junction between said base shell and bulb forhermetically sealing the space therebetween to prevent leakage of airinto said enclosure through the interior of said lamp base.

6. A light projecting device comprisingan airtight enclosure, anelectric lam-p sealed within said enclosure comprising a bulb having aneck portion and a base having a shell portion enclosing said neckportion and secured thereto, said base extending out through the wall ofsaid enclosure and hermetically sealed thereto, and a. sealing compoundcomposed of urea formaldehyde modified with a nondrying alkyd disposedadjacent the junction between said base shell and bulb for hermeticallysealing the space therebetween to prevent leakage of air into saidenclosure through the interior of said lamp base.

7. An electric lamp comprising a bulb having a. neck portion and a baseenclosing said neck portion and secured thereto by a composite basingcement having portions of different compositions, one of said portionsbeing of a composition providing a. bond of the required mechanicalstrength between said base and bulb to hold said parts together and theother of said portions being of a. composition providing a hermetic sealbetween said base and bulb, the second mentioned .portion being composedof a thermo-setting gum modiiied with a nondrying material whichinhibits brittleness.

JUNIUS DANA.

